Mixer



June 4, 1957 J. c STERRlTT 2,794,626

MIXER Filed May 8, 1952 3 Sheets-Sheet 2 IN V EN TOR. .7a% (2 526/212?June 4, 1957 J. c. STERRITT MIXER Filed ma 8. 1 952 3 Sheets-Sheet 3INVENTOR. 72%;? Z 5.5212275 United States Patent man 5 Application May8, 1952, Serial No. 286,735.

8 Claims. (ill. 2591l4) The present'invention relates tomixing machines,and particularly to material mixers adapted for industrial uses.

Many industrial processes involve the mixing or working ofmaterialsfor'the purpose of producingv greater homogeneity orof insuringthat a chemical or physical re-' action occurs uniformly throughoutagiven:mass of the material. Since the viscosity and. othercharacteristics of the materials which must be dealt withvaryrwidel'y,.it is a common experience to find that a given materialcannotbe satisfactorily mixed by a type ofzmixer which may be themost'efficient for mixing another material; Moreover, some'materials maybe mixed by. a wide variety of types of mixers, while other materialswhich are more difficult to mix can only be mixed by a few or only asingle known'type. Frequently diiferentm-aterials in this class require,different types of mixers. Finally, there are 0 some materials, such aschicle (which mustbe 'thoroughly worked during. a washing operation),eth'ocell emulsions, somepigments, resins and other materials which arevery diflicult. to' deal with" in any previously known type of mixingmachine, since they require prolonged mixing treatments" and frequentlynecessitate high expenditures of power.. There is a need, therefore, fora heavy-duty mixer which will operate efliciently and effectively onenumber of.;the.materials which are diflicult to The general classof'mixers which have been used most extensively on materials that arediflicult'to work or mix arethose in which the mixer comprises asuitable housing having. a pair of oppositely rotating shafts equippedwith mixing blades. The blades are so arranged that any singletransverse plane intersects two blades on each shaft, and the blades .ofeach shaft in that plane are diametrically opposed to eachother. Threetypes of'mixers within that general class have been used, as follows:first, those in which the blades on the two shafts overlap (i. e. arelonger than one half the distance between the shafts) and the shaftsrotate at the same speed (see-U. S. P atent No;. 1,563,524); second,those in-which the blades do not overlap and'the shafts are rotated atany desired different speeds (see U. S. Patents Nos. 1,364,401 and1,989,126); and third, those'in which the blades overlap and one shaftrotates atexactly twice the speed of the other (see U. S; Patents1,004,908 and 2,095,907. Patent 913,133 dis.- closes a similar mixerexcept that one blade is omitted onone shaft.)

Another general class of mixers which have been used have overlappingblades on parallel shafts with four blades on each shaft in asingle'transverse plane; Inthis class of mixerthe shafts always rotateat the samespeed. They do not provide as effective a mixing action onheavy materials as do mixers in which the speeds of the shafts differ,and the permissible amount of blade overlap is somewhat restricted.

A third classification of prior mixers comprises a mixer having twodiametrically opposed blades on one shaft and four equally spacedbladeson the other, with the two bladed shaft rotated at: twice the speed ofthe four bladed 2. shaft. The blades fully overlap.Thistypeofmixerperforms an: effective mixing function butrequires asubstantial power input.

ltihas been observed. that overlapping blades provide enhanced mixingandithat some difference .in the speeds of the shafts also aids in theperformance of the mixing function. However, ifthe difference in speedsis as much as two to "one, thepower requirements of the mixer aresubstantially increased, all other things being equal. It has also beenrecognized that within limits an increase in the number of bladesincreases .the mixing action but also the power requirements; andanincrease in the number of blades tends to reduce the permissible amountof blade overlap.

It is the general object of the present invention to provide a fourthclass of mixer which will achieve the optimum of mixing effect foragiven power expenditure and which'is peculiarly suited for use on:chicle and other materials which are diflicult to mix. This objectiveis realized by employing the maximum number of blades which will overlapto the maximum extent with a relatively small difierencebetweenthe-speeds of the two shafts. More specifically, the arrangementinvolves the use of two diametrically opposed blades on one shaft andthree equally spaced blades on the other, with the two bladed shaftdriven atone and one half times the speed of the three bladed-shaft.It-is found that such a mixer may be used successfully on a Wide varietyof materials which are diflicult to mix; will mix some materials thatcannot be mixedby either of the first two classes of mixers referredtoabove; and requires substantially less, power than the third class ofmixer mentioned for an equivalent mixing job.

The 'blades closely fit'the bottom and end walls of the housing to avoidthe-formationof pockets or layers of material which might not be actedon by the blades. For the same reason, the blades overlap eachother tosuch an extent that the outer edges of the blades on.-one shaft passclose to the other shaft. As a result of this arrangement and the factthat the; shafts are moving at different speeds, material is trappedbetween adjacent blades and between the blades and the bottom of thehousing and is subjected to a squeezing action. This squeezing actionwill tend to extrude the trapped material through the running clearancesat the ends of the blades and" the ends of the housing, but since theseclearances are preferably made as smallas possible, "heavy materialscannot escape with the required rapidity and hence excessive pressureswill develop and it'willybe substantially impossible to drive the mixerat a useful speed. While this difliculty may be overcome by providingnotches in the ends of'the blades, the notches in each blade beingdisplaced axiallywith respect to the notches in other blades on the sameshaft, it is preferred to provide openings in the blades themselves. Theextrusion of the material through these openings duringthe mixingoperation greatly enhances the mixing function and constitutes a majorfactor contributing to the improved efiiciency of the mixer.

The blades are preferably curved forwardly at their outer extremities toresist the natural tendency of the material to-slide outwardly along thefaces of the blades. This also provides-a hooking action which will drawmaterial down between the two shafts.

Inthe preferred embodiment of the invention shown, three axially spacedsets of blades are provided within the housing. The two sets at' theends of the housing have blades which are so inclined with respect tothe axes of the shafts that they tend to feed material toward the centerof the'housing: This enhances the mixing action.

Other objects, features, and advantages of the present v V 7, 3invention will become apparent from the subsequent description, taken inconjunction with the accompanying drawings. V l

-i .Inithfdrawingsinw j l'l- V Q Figure l is aside e'levational.viewof'the mixer, showing the supporting base and the driving motor; 3Figure 2 is an end elevational view of the apparatus of Figure l withthe end guard plate removed, and showing the tilting mechanism; i 1

Figure 3 is a cross-sectional View. taken along the line 3-3 of Figure2, and showing'the mixer blades and the supporting means for the bladeshafts; i

Figure 4 is a cross sectional view taken along the line 4-4 of Figure 3and showing the configuration of the central sets of blades; and

Figure 5 is a cross-sectional view taken along the line 5-5 of Figure 3and showing the configuration of the outer sets of blades.

The mechanism comprises in general a container or trough 11 for holdingthe batch of material to be mixed, a supporting stand 12 supporting thetrough assembly for pivotal movement about a horizontal axis, and adriving motor 13 supported on a base 14 and operatively connected to theblade shafts. The trough 11 comprises an inner Wall 15 of generallyU-shaped cross-section and an outer shell 16 which surrounds the innerwall, forming a jacket 17 therebetween to hold a cooling medium or thelike. In the illustrated embodiment, the outer shell 16 is joined withwall 15 along its upper edges 18 and side edges 19, and the jacket isprovided with a drain opening 20. The ends of trough wall 15 are closedby end plates 21 and 22 which are secured thereto by means of flanges 23and 24 at the opposite ends of wall 15.

The trough 11 is supported at the opposite ends by a pair of bearingsupports 25 and 26 which extend up- Wardly from base 12. These bearingsupports are provided with bearings 27 and 28 respectively at theirupper ends, and a pair of trunnions 29 and 31 are secured to theopposite ends of trough 11 and are journaled within these bearings.Trunnion 29 is secured outwardly of end plate 21 by a bracket structure32, and trunnion 31 is secured to the outer end of a gear housing 33which in turn is supported by the trough. Housing 33 is secured to theend plate 22 through the intermediary of a bearing "supporting framework34 which is secured to and extends from end plate 22. As will be seenlater, bearingsupport 34 serves to hold the bearings for the bladeshafts.

The trunnions 29 and 31' are annular in shape and serve as bearingsupports for a blade shaft 35 which extends through the trough andserves to support the front blades therein. In particular, theoppositeends of shaft 35 are provided with bushings 36 and'37 which are disposedwithin trunnions 29 and 31 respectively, so that the shaft is freelyrotatable independently of the position of the trough. The end of shaft35 adjacent bearing support 26 is connected to driving motor 13, througha coupling 38; a

Means are provided for tilting the trough assembly for receiving ordumping material, and this means preferably comprises a worm gearquadrant 39 keyed to trunnion 29 outwardly of bearing 27. A guard 40supported by base 12 is provided to cover the worm gear quadrant 39 andits adjacent parts. A worm 41 is supported on base 12 by means ofbearings 43 and 44 for rotation about a horizontal axis, this wormmeshing with worm gear quadrant 39, and a hand crank 45 allows the worm,to be rotated, thus rocking the entire, trough about the axis of shaft35. A stop 46 may be provided on the base for positioning the trough. 7j I The trough is also provided with a second .shaft47 parallel to shaft35 for supporting the rear blades. Shaft 47 is supported at its oppositeends by bearings 48 and 49, bearing '48 being secured. outwardly of t hetrough "by means of bracket structure 32. Bearing 49 is supported bybearing support 34, this hearing support also supportand held in placeby an end cap 55. Shaft 47 is likewise provided with a thrust plate 56disposed within a recess in bearing 48 and held in place by a cap 57. Inorder to prevent leakage of the material from the trough, glands 58 areprovided on shafts 35 and 47 secured to the trough end plates 21 and 22.In Figure 3, the glands 58 on the left hand side are shown in verticalcross-section to make visible their attaching bolts 59.

As stated previously, motor 13 is coupled to front blade shaft 35 andthis shaft is provided with a gear 61 within gear housing 33. Gear 61meshes with a gear 62 secured to the end of rear shaft 47 within thegear hous ing. These gears may'be conventional spur gears, and the ratioof their teeth is such that shaft 47 makes one and one half revolutionsper revolution of shaft 35. Of course, other types of gearing may beused if desired to achieve this ratio.

The sets of blades are best shown in Figures 3, 4 and 5, and in theillustrated embodiment the blades on shaft 35 are termed the front bladmand the blades on shaft 47 the rear blades. It will be seen that in theillustrated embodiment each shaft'has three sets of blades; inparticular, front shaft 35 has a central set of blades 63 and an outerset of blades 64 on either side thereof, and shaft 47 is provided with acentral set of blades 65 and an outer set of blades 66 on either sidethereof. As seen in Fi-gures'4 and 5,. the blade sets are preferablyprovided with hubs which are keyed to shafts 35 and 47. Blade set 63comprises a pair. of diametrically opposed blades 67, while blade set 65on shaft 47 comprises three equally spaced blades 68. Preferably, theseblades are curved slightly forward at their outward portions in thedirection of rotation; that is, blade 67 is curved slightly clockwiseand blades 68 slightly counterclockwise as shown in Fig. 4. Blades 67and 68 are preferably aligned in an axial direction with the axes oftheir respective shafts, and the blades are so positioned on the shaftsthat, as seen in Fig. 4, when a particular blade 68 liessubstantially ona line intersecting the shaft axes, blades 67 will be substantiallyperpendicular to this line. It will be seen that since shaft 35 rotatesat one and one half times the speed of shaft 47, the blades 67 will passbetween the blades 68 during operation, while moving at a faster ratethan blades 68. a Y t The blade sets 64 on shaft 35 and the blade sets66 on shaft 47 are each symmetrically disposed about their respectivecentral blade sets, but are offset from the central sets in acircumferential direction. Each. blade set 64 comprises twodiametrically opposed blades 69, and each blade set 66 includes threeequally spaced blades 71. Like the central blades 67 and 68, blades 69and 71 are also curved forwardly at their outer ends as shown in Figure5. However, these blades are of skew shape with respect to their shafts,so that the outer edges 72 of blades 69 and the outer edges 73 of blades71 form portions of helices around their shaft axes. These shapes,during rotation of the shaft blade sets 64and 66, 'will tend to forcethe material from the end plates ;21' and 22 of the trough toward thecentral portion of the trough,

Preferably, the clearance 74 between the ends of blade sets 64 and-66and the end plates 21 and 22 of the trough are so small that littlematerial can be forced between the end plates and the blade ends. Thebottom of trough 15 is of a doubly curved shape to conform to the pathof theblades. In particular, the'trough bottom is provided with aconcave portion 75 concentric with the axis of shaft 35, and a concaveportion 76 concentric with the axis of shaft 47. The clearances betweenthe edges of the blades and the curved portions 75 and 76 are so smallas to prevent the formation of pockets or layers of material which maynot be acted upon by the blades. The blade widths are such, relative tothe distance between shafts 35 and 47, that the blades overlap to aconsiderable extent, the outer edges of the blades on one shaft passingclose to the hub of the blades on the other shaft.

In order to prevent excessive pressure between the blades duringoperation, eachblade is preferably provided with an opening 77 throughwhich the material trapped between adjacent blades may pass. It will beappreciated that since the shafts are moving at different speeds,material trapped between adjacent blades and between the blades and thehousing are subjected to a squeezing action and that heavy materialscannot escape between the blade ends and the walls of the trough becauseof the small clearances. The extrusion of the material through openings77 therefore greatly improves the efliciency of the mixer especiallywhen used with heavy materials. Although the openings 77 are shown asrectangular in shape in the illustrated embodiment, other shapes ofopenings may of course be used.-

In operation, the material to be mixed is placed in the trough and ifnecessary the blades'may be jogged back and forth in order to allow thematerial to settle more compactly in the trough. The motor 13 is thenstarted, driving shafts 35 and 47 in opposite directions as seen inFigures 4 and 5, shaft 35 running at one and one-half times the speed ofshaft 47, and blade sets 63 and 64 on shaft 35 will cooperate with bladesets 65 and 66 on shaft 47 to mix the material. The blade sets will movein the direction of the arrows in Figures 4 and 5, with the bladesmoving downwardly between the shafts. Since front shaft 35 is rotatingat a higher speed than rear shaft 47, as each front blade passes betweentwo rear blades, it will force the material ahead of it against the backsurface of a rear blade. At the same time, the skew shaped side bladeswill continuously circulate material from the sides to the centralportion of the trough. In this manner a thorough and eflicient mixingaction takes place between the blades.

While it will be apparent that the preferred embodiment of the inventionherein disclosed is well calculated to fulfill the objects above stated,it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the properscope or fair meaning of the subjoined claims.

What is claimed is:

1. A mixer having a housing, a pair of parallel shafts journaled in saidhousing, and mixing blades on said shafts, there being in a singletransverse plane two generally radial and diametrically opposed bladeson one of said shafts and three equally spaced generally radial bladeson the other, the radial length of each of said blades being sufficientto cause the blades to overlap and their outer edges to sweep in closeproximity to the hub of the blades on the other shaft, and means forrotating said shafts in opposite directions with the speed of the twobladed shaft one and one half the speed of the three bladed shaft, saidblades being so fixed on said shafts and the shafts so interconnectedthat in said transverse plane the radial line of a blade on the twobladed shaft is substantially perpendicular to the line intersecting theaxes of the two shafts when the radial line of one of the blades of thethree bladed shaft lies approximately in the line intersecting saidshafts.

2. A mixer having a housing, a pair of parallel shafts journaled in saidhousing, and mixing blades on said shafts, there being in a singletransverse plane two generally radial and diametrically opposed bladeson one of said shafts and three equally spaced generally radial blades,on the other, the radial length of each of said blades being sufficientto cause the blades to overlap and their outer edges to sweep in closeproximity to the hub of the blades on the other shaft, and means forrotating said shafts in opposite directions with the blades on bothshafts moving downwardly between the shafts and the speed of the twobladed shaft one and one half the speed of the three bladed shaft, saidblades being so fixed on said shafts and the shafts so interconnectedthat in said transverse plane the radial line .of a blade on the twobladed shaft is substantially perpendicular to the line intersecting theaxes .of the two shafts when the radial line of one of the blades of thethree bladed shaft lies approximately in the line intersectingsaidshafts.

3. A mixer having a housing, a pair of parallel shafts journaled in saidhousing, and mixing blades on said shafts, there being in a singletransverse plane two generally radial and diametrically opposed bladeson one of said shafts and three equally spaced generally radial bladeson the other, the radial length of each of said blades being sufficientto cause the blades to overlap and their outer edges to sweep in closeproximity to the hub of the blades on the other shaft, and means forrotating said shafts in opposite directions with the speed of the twobladed shaft one and one half the speed of the three bladed shaft, saidblades being so fixed on said shafts and the shafts so interconnectedthat in said transverse plane the radial line of a blade on the twobladed shaft is substantially perpendicular to the line intersecting theaxes of the two shafts when the radial line of one of the blades of thethree bladed shaft lies approximately in the line intersecting saidshafts, the bottom of said housing being formed to lie in closeproximity to the paths of movement of said blade tips below the planecommon to said shafts.

4. A mixer having a housing, a pair of paraliel shafts journaled in saidhousing and mixing blades on said shafts, there being in a singletransverse plane two generally radial and diametrically opposed bladeson one of said shafts and three equally spaced generally radial bladeson the other, the radial length of each of said blades being sufficientto cause the blades to overlap and their outer edges to sweep in closeproximity to the hub of the blades on the other shaft, and means forrotating said shafts in opposite directions with the blades on bothshafts moving downwardly between the shafts and the speed of the twobladed shaft one and one half the speed of the three bladed shaft, saidblades being so fixed on said shafts and the shafts so interconnectedthat in said transverse plane the radial line of a blade on the twobladed shaft is substantially perpendicular to the line intersecting theaxes of the two shafts when the radial line of one of the blades of thethree bladed shaft lies approximately in the line intersecting saidshafts, the bottom of said housing being formed to lie in closeproximity to the paths of movement of said blade tips below the planecommon to said shafts.

5. A mixer having a housing, a pair of parallel shafts journaled in saidhousing, and mixing blades on said shafts, there being in a singletransverse plane two generally radial and diametrically opposed bladeson one of said shafts and three equally spaced generally radial bladeson the other, the radial length of each of said blades being suflicientto cause the blades to overlap and their outer edges to sweep in closeproximity to the hub of the blades on the other shaft, and means forrotating said shafts in opposite directions with the speed of the twobladed shaft one and one half the speed of the three bladed shaft, saidblades being so fixed on said shafts and the shafts so interconnectedthat in said transverse plane the radial line of a blade on the twobladed shaft is substantially perpendicular to the line intersecting theaxes of the two shafts when the radial line of one of the blades of thethree bladed shaft lies approximately in the line intersecting saidshafts, the bottom of said housing being formed to lie in closeproximity to the paths of movement of said blade tips below the planecommon to said speed of the two bladed shaft one and one .of the threebladed shaft, said blades being so fixed on shafts, said blades havingopenings therein through which material may extrude during the mixingoperation.

6. A mixer having a housing, a pair of parallel shafts journale'd insaid housing, and mixing blades on said shafts, there being in a singletransverse plane two generally radial and diametrically opposed bladeson one or said shafts and three equally spaced generally radial bladeson the other, the radial length of each of said blades being sufficientto cause the blades to overlap and their outer edges to sweep in closeproximity to the hub of the blades on the other shaft, and means forrotating said.

shafts in opposite directions with the blades on both shafts movingdownwardly between the shafts and the said shafts and the'shafts sointerconnected that in said transverse plane the radial line of a bladeon the two bladed shaft is substantially perpendicular to the lineintersecting the axes of the two shafts when the radial line 1 of one ofthe blades of the three bladed shaft lies ap roximately in the lineintersecting said shafts, the bottom of said housing being formed to liein close proximity to the paths of movement of said blade tips below theplane common to said shafts, said blades having openings therein throughwhich material may extrude during the mixing operation.

half the speed 1 7,

7. A mixer as defined iniclaim 1 in which there are 'two sets ofcooperating bladeson said shafts, one set being located at each end ofsaid shafts and eachjset being identical except that the blades areinclined with respect tothe axes of the shafts so that the blade tipslie in a helix with the helix angle of one set opposite to that of theother and the angular position of the blades tends to work material awayfrom the ends of the shafts.

*8. A mixer as defined in claim 7 in which there is a third set ofcooperating blades on said shafts disposed between said first two sets,the blades of said third set lying in planes substantially parallel totheir respective shaft axes.

References Cited in the file of this patent UNITED STATES PATENTS

